Field of Invention
The present invention relates to an improved chill roll apparatus for setting ink to a web of paper. Typically, in a web fed printing press, a continuous sheet or web of paper exits the printing press and is then subject to a tension control unit and a web aligner. Next, the web is passed through an oven to remove or drive off the chemical solvents from the ink. However, the elevated temperature of the oven prevents the ink from drying on the web so the web is then passed through a series of chill rolls to cool the web and to set the ink to the paper. Subsequently, the web is fed to a slitter or cutter for further processing.
A basic chill roll apparatus consists of a series of rollers, typically four, arranged in a stacked offset manner beneath the plane of the web. The web serpentinely traverses its way around the chill rolls in order to cool the web and set the ink to the paper. A coolant, such as water, is circulated through the chill rolls to constantly supply the chill rolls with a fresh supply of coolant. The path of the coolant further includes some type of heat exchanger to rejuvenate and recool the heated coolant after it passes through the chill rolls.
In a conventional chill roll apparatus the solvents inks and printing resins or printing residue used and produced in the printing process can attach to and build up on the chill rolls themselves. This problem is created by a layer of air, containing the solvents and residue, forming on the upper and lower surfaces of the web and becoming trapped between the web and the chill rolls thereby allowing the solvents and residue to transfer onto the chill roll. When the printing residue collects on the chill rolls, the residue is transferred back to the web and marks or smears the freshly printed web. By either significantly reducing the barrier or boundary layer of air which has formed on the web or by removing the solvent fumes, inks and printing residue from this barrier layer, the printing residue cannot attach to the chill rolls and cannot ruin the printed web.
The oven is used to drive off the wet solvents and resins from the inks used during the printing process. The heated environment causes the solvents and resins to evaporate and lift off the face of the web. However, as the web of paper travels from the oven to the chill rolls, a barrier or boundary layer of air attaches to both surfaces of the web. The creation, existence and size of the barrier layer is a function of the web speed and tension and the type of paper being employed. The faster the web moves or the less the tension of the web, the larger the barrier layer grows and the greater adherence it has to the web. Consequently, as the web travels through the oven and the solvents, resins and printing residue lift off the web, the barrier layers of air become impregnated with the solvents and residue.
In a conventional chill roll apparatus, after the heated web leaves the oven, the web typically travels a short horizontal distance to a first chill roll and wraps downwardly around this chill roll. While the arrangement of chill rolls may either be above or below the plane of the web exiting oven, for illustrative purposes, a conventional chill roll apparatus will be described herein as having the series of chill rolls disposed below the plane of the web. Because the barrier air surrounding the web is at an elevated temperature, as the web exits the oven into ambient air, the solvent laden warmer barrier layer lifts off the top of the web and is replaced by cleaner ambient air. However, the barrier layer of air which has attached to the bottom or underneath side of the web is prevented from rising by the web itself and, therefore, the lower barrier layer becomes trapped between the web and the chill roll as the web wraps downwardly around the first chill. The trapped barrier layer then transfers the ink solvents and other trapped printing residue onto the chill roll which, in turn, transfers this ink residue back to the web causing marking or smearing on the printed web.
Various types of chill roll apparatuses for setting ink to the web are presently used. The conventional method of chilling a web makes use of four chill rolls, arranged in a stacked offset grid. The web traverses the grid of chill rolls so that both surfaces of the web alternately contact the chill rolls in order to achieve chilling of the web. Generally, the web travels from the oven and wraps over the top of the first chill roll so that the underneath side of the web is in contact with the chill roll. As explained above, the barrier layer adhering to the lower surface of the web is prevented from naturally dissipating as a result of the position of the overlying web and the barrier layer becomes trapped between the web and the first chill roll as the web traverses the chill roll. After passing over the first chill roll, the web is fed downwardly to the second chill roll disposed beneath the first chill roll. The web wraps around the second chill roll so that the top surface of the web is now in contact with the chill roll rather than the bottom surface. Even though the heated barrier layer on the top of the web could rise off the surface of the web after exiting the oven, due to the speed or tension of the web a solvent laden barrier layer of air still adheres to the upper surface of the web. As a result, this solvent layer becomes trapped between the upper surface of the web and the second chill roll. The web is then fed diagonally upwardly to the third chill roll disposed in a plane slightly below the first chill roll. In wrapping around the third chill roll the lower surface of the web engages the surface of the chill roll and the barrier layer which is adhering to the lower surface becomes trapped between the lower surface of the web and the third chill roll. The web is then finally fed downwardly to a fourth chill roll disposed beneath the third chill roll so that the upper surface of the web contacts the chill roll. Here, as with the other chill rolls, the barrier layer adhering to the web becomes trapped between the web and the chill roll.
The inherent problem in such conventional methods is that the solvent laden barrier layer adhering to either side of the web becomes trapped at the nip formed where the web wraps around each chill roll and, as a result, the solvents and ink resins suspended in the barrier layers transfer to the surface of the chill rolls. Consequently, as the web continuously travels through the chill roll apparatus, the ink residue on the chill rolls marks and smears subsequent portions of the web and subsequent sections of residue laden barrier layers continue to deposit ink residue on the surfaces of the chill rolls. As can be seen, this is a self perpetuating problem which can potentially ruin an entire printed web of paper causing substantial waste and expense.
In an effort to solve this problem, other prior art devices have added a tunnel extending from the oven to the first chill roll to assist solvent disbursement. By maintaining the oven at a decreased pressure, in comparison to the ambient air outside the oven, a suction is created which draws external ambient air into the tunnel in a direction opposite to the movement of the web and any barrier layer which may have formed. Unfortunately, this method, at best, is only effective in minimally reducing the solvent laden barrier layer and does not significantly eliminate the solvent laden barrier layer.
Still further prior art systems disclose a fan for blowing air across the web as it comes out of the oven in an attempt to dissipate the solvent laden barrier layer or to replace the suspended solvents and resins in the barrier layer. Such ventilating systems are less efficient as the speed of the web is increased. The inherent problem with such a fan system is that the fan has to be very powerful and, consequently, expensive in order to overcome the adherence of the barrier layer to the web.
In another prior art apparatus, the chill rolls are arranged above the plane of the web rather than below and are located a further distance from the oven. The longer travel distance from the oven to the first chill roll works to decrease the solvent in the barrier layer on the top of the web by providing a longer time for the barrier layer to naturally dissipate. Moreover, because the web then wraps upwardly around the first chill roll, the barrier layer which has formed to the bottom of the web undergoes some natural dissipation as the web turns upward to wrap around the first chill roll. However, this natural dissipation is not effective enough in significantly reducing the barrier layer.
A still further improvement of this system over previous methods mounts the four chill rolls in a frame which pivots about the axis of the first chill roll. The pivoting action allows the second chill roll to be placed closely adjacent and in overlying registration with the web travelling to the first chill roll from the oven. Because the rotation of the second chill roll is in a direction opposite that of the web travelling from the oven to the first chill roll, the barrier layer adhering to the top surface of the web exiting the oven may be subjected to the opposing movement of the web traversing the second chill roll in the opposite direction depending upon placement of the second chill roll. As best understood, this opposing motion causes the barrier layer adhering to the web to be reduced in size.
In spite of these improvements, this method does not effectively solve the solvent and resin laden barrier layer problem. In this last described apparatus, only the barrier layer on the top surface of the web is subject to cleaning. The barrier layer that is formed on the bottom of the web and subsequently trapped between the web and the second chill roll is not acted upon at any time. Instead this bottom barrier layer is subject only to natural dissipation. Consequently, at least two of the four chill rolls still become marked and the bottom portion of the web is continuously subjected to these marked rollers. Moreover, it is possible that the opposing action of the web traversing the second chill roll and the web travelling to the first chill roll is insufficient to effectively remove the barrier layer. Significant solvents and residue may remain and adhere to the first chill roll and subsequently ruin the other side of the web as well. This results in just as much waste as if the entire web were ruined.
The pivoting frame also gives rise to a further problem. As the chill roll frame is rotated about the first chill roll to position the second chill roll further from the surface of the web exiting the oven, the wrap of the web about the first chill roll is decreased. Decreased contact with the chill rolls reduces the cooling effectiveness of the apparatus.
The present invention overcomes the problems and limitations associated with these prior systems by employing a chill roll apparatus in which the second and third chill rolls are mounted on adjustable shafts or eccentrics such that both the second and third chill rolls can be positioned to scrub or clean the residue laden barrier layers of air on both sides of the web. While applicant understands the result of this scrubbing is to significantly reduce the barrier layers, thereby reducing the amount of solvents and ink residue, testing and experimentation has proved inconclusive except for the fact that ink buildup on the rollers and subsequent smearing of the web is drastically reduced. It is also possible that instead of reducing the barrier layers, the scrubbing removes the solvent and ink laden air and replaces it with clean ambient air. The resulting effect of reducing buildup on the chill rollers would be the same.
Because the second and third chill rolls are adjustably positionable, both vertically and horizontally, the second chill roll can be positioned essentially in contact with the web travelling from the oven to the first chill roll. In this manner, maximum wrap of the web about the first chill roll is achieved. Similarly, by lowering the third chill roll closer to the web travelling between the first and second chill rolls, maximum wrap of the web about the second chill roll is achieved. Clearly, as greater surface contact between the web and the chill rolls is achieved, the cooling efficiency of the chill roll is increased thereby providing better setting of the ink to the web.
The vertical adjustability of the second and third chill rolls also allows the operator to vary the degree or amount of scrubbing. Rather than positioning the second and third chill rolls adjacent and slightly above the portions of the web to be scrubbed, wherein the amount of effective scrubbing would be limited, the second and third chill rolls can be positioned so that the two portions of web involved are in contact. As a result, an increased zone of interference or scrubbing is created which increases the scrubbing efficiency of the present invention and, additionally, achieves greater web wrap efficiency and cooling.